1. Field of the Invention
This invention relates to an image forming apparatus for forming copy images of reflection originals such as documents or books which is endowed with the function of forming a copy image of a transmitting original such as a slide film or the like.
2. Description of the Prior Art
In a copying apparatus capable of copying not only ordinary reflection originals but also transmitted enlarged projected images of a slide film (hereinafter referred to as the combination copying apparatus), optical alignment for obtaining copies of the transmitted enlarged projected images of the slide film has been very difficult. This will hereinafter be described in detail by reference to FIGS. 1 and 2 of the accompanying drawings. In FIG. 1, reference numeral 50 designates a copying apparatus body, reference numeral 4 denotes an original supporting glass plate provided on the copying apparatus body 50, and P designates a slide projection device. The projection device P has a Fresnel lens 108, a reflecting mirror 107 for changing the optical path, a projection lens 109 for enlargedly projecting a slide film, and an illuminating portion 110 for holding the slide film 105 and illuminating it. The device P is removably mounted on the apparatus body 50. A photosensitive drum 1 and an optical system including a lens 8 are disposed within the copying apparatus body 50, as shown in FIG. 2, but these are not shown in FIG. 1. In FIG. 2, reference numeral 105 designates the slide film, and reference numeral 109 denotes the projection lens of the slide projection device P. In such a conventional combination copying apparatus, during the copying of an ordinary reflection type original, the bulky and weighty slide projection device including the reflecting mirror 107, the Fresnel lens 108 and the illuminating device 110 must be removed and moved from the original supporting glass plate 4 and thus, the change-over operation thereof has been cumbersome. Also, before the projected image of the slide is copied, the slide film 105 which is an original must be loaded into the projection device P and the point of focus must be adjusted on the upper surface of the original supporting glass plate 4 by the projection lens 109.
This has led to the necessity of the procedures of removing the Fresnel lens 108 on the original supporting glass plate 4, placing a sheet of white paper on the original supporting glass plate 4, projecting an image onto the white paper and adjusting the point of focus, thereafter removing the white paper from the original supporting glass plate 4 and adjusting the optic axis of the Fresnel lens 108. Alternatively, it is also conceivable to observe the point of focus by a projected image falling on the frame-like white paper for setting the copying area existing between the Fresnel lens 108 and the original supporting glass plate 4, but it is dangerous to adjust the point of focus in the marginal portion of the slide film 105 which lies outside the copying area, because it is very rare that the focused surface of the original lies around the slide film 105.